Conventionally, an impact tool, which transmits a rotational force of a motor to a hammer and applies a striking force in a rotational direction to a tool support member using the hammer, has been known, and such an impact tool is described in Patent Document 1. The impact tool described in Patent Document 1 includes: a housing; a motor provided inside the housing; a spindle to which a rotational force of the motor is transmitted; a first cam groove provided in an outer circumferential surface of the spindle; a cylindrical hammer attached to an outer circumference of the spindle; a first engaging portion provided in the hammer; a second cam groove provided in an inner circumferential surface of the hammer; a cam ball held by the first cam groove and the second cam groove; a tool support member rotatably supported by the housing; a second engaging portion provided in the tool support member; and a spring as an elastic member which presses the hammer toward the tool support member. A tightening tool is attached to the tool support member. The tightening tool is provided with a concave portion that a head portion of a screw member enters.
When a rotational force of the motor is transmitted to the spindle, the rotational force is transmitted to the hammer via the cam ball and transmitted to the tool support member via the first engaging portion and the second engaging portion, thereby tightening the screw member. When a rotational force required to tighten the screw member is small, the hammer does not move in an axial direction of the spindle and the first engaging portion does not climb over the second engaging portion.
On the contrary, when the rotational force required to tighten the screw member increases, the hammer moves in the axial direction of the spindle and in a direction of separating from the tool support member against a force of the elastic member, and the first engaging portion climbs over the second engaging portion. Then, the hammer moves in the axial direction of the spindle and in a direction of approaching the tool support member by the force of the elastic member, and the first engaging portion strikes the second engaging portion. In this manner, a striking force in the rotational direction is applied from the hammer to the tool support member.